We have a washing machine in the brain

One of the best known methods of torture is sleep deprivation. The consequences are familiar to all of us who are parents. You wake up the next day thinking that nothing good can happen that day. You drag yourself down to your daily chores, with one of the biggest downfalls the possibility of two or three such nights of bullfighting.

Sleep stands for the good functioning of our cognitive and emotional capacities, as well as other less well-known functions. As recently discovered, it plays a crucial role in removing substances that accumulate in the brain. Yes, folks, we also run the washing machine at night.

Why is cerebrospinal fluid vital for brainwashing?

Previous studies suggest that cerebrospinal fluid, the one that surrounds and immerses the central nervous system – the spinal cord and brain – is critical in removing toxins produced or accumulated there. This has led to one of the most surprising discoveries of recent years.

In 2019, Laura Lewis's team in Boston published a study whose representative video (see below) went around the world for its beauty: in it, a flow of blood, rich in oxygen (in red), expands like a wave. Immediately afterward, another rush of cerebrospinal fluid (in blue) appears in the so-called fourth ventricle, in the lower part of the brain. All this happens when we sleep, over and over again.

To carry out this study, the researchers used functional MRI - a technique to look at how the brain works with big magnets - to monitor the sleep of 13 people aged between 23 and 33. Their paper, published in the prestigious journal Science, shows how the slow waves characteristic of sleep are coupled to hemodynamic blood and cerebrospinal fluid waves. It works as if the brain had a self-washing function, like a washing machine, but without detergent or coins.

Here we can see the brain washing, in a video shared by Lewis and Boston University:

“There are a lot of people who are happy to participate because they want to be paid to sleep,” Lewis laughs. “But it turns out that their job is actually – secretly – almost the hardest part of our studio. We have all this fancy equipment and complicated technologies, and often a big problem is that people can't fall asleep because they're in a very loud metal tube, and it's a strange environment.”

How has this story continued?

Lewis's group thought that this brain function could be hacked to induce washouts at will. In March 2023, they published a new paper, this time in the journal PLOS Biology, describing a stimulation kit capable of switching on the brainwasher. Surprisingly, they achieved this while the people they tested it on were... awake! They used a type of stimulation sometimes used in similar experiments: a kind of radial checkerboard that researchers use to make brain responses more visible in a functional MRI session.

The washing process was not exactly the same as the one described during sleep, but it was similar enough. They could activate the brainwasher with a visual stimulus, almost like a switch. In this latest paper, the researchers say they want to apply these findings to brain disorders such as Alzheimer’s, in which cerebrospinal fluid is thought to play a critical role. This will allow them to see what is in there and give a quick answer about the effects or possible treatments.

Interestingly, this image has stuck in my mind. I am guessing I would benefit from a thorough wash, with intensive centrifugation, and even a pleasant drying in the sun more than once.

To know more:

Fultz, N. E., Bonmassar, G., Setsompop, K., Stickgold, R. A., Rosen, B. R., Polimeni, J. R., and Lewis, L. D. (2019). Coupled electrophysiological, hemodynamic, and cerebrospinal fluid oscillations in human sleep. Science, 366(6465), 628-631.DOI:10.1126/science.aax544

Williams SD, Setzer B, Fultz NE, Valdiviezo Z, Tacugue N, Diamandis Z, et al. (2023) Neural activity induced by sensory stimulation can drive large-scale cerebrospinal fluid flow during wakefulness in humans. PLoS Biol 21(3): e3002035. DOI:10.1371/journal.pbio.3002035

Benson K, (2019) Are We “Brain Washed” during Sleep? The Brink, Boston University.